JP2002307605A - Coated steel panel excellent in draw squeezing processability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated steel panel obtained by forming the coating film of a thermosetting resin on a plated steel panel, forming no large unevenness in its plating layer and having a coating film hard to lower glossiness even if processing bringing about the deformation of the plating layer and the elongation of the coating film is applied. SOLUTION: The coating film of the thermosetting resin, wherein the elastic modulus of the uppermost resin coating film at 20 deg.C is 1×10<3> -5×10<3> N/mm<2> , is provided on the molten Zn-Al type plating layer containing 2-65 mass % of Al of the plated steel panel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated steel sheet excellent in deep drawing workability used for exterior members such as home appliances and heating equipment, motor cases and various parts cases.

[0002]

2. Description of the Related Art Precoated steel sheets can be manufactured only by cutting and processing, so that they have been conventionally used for manufacturing exterior members or articles such as home electric appliances and heating equipment. This pre-coated steel sheet is mainly used in which a thermosetting resin primer layer is formed on a steel sheet and an overcoat layer of the thermosetting resin is formed thereon. For example, a coating film of a polyester resin or an epoxy resin is used for a primer layer, and a coating film of a high molecular polyester resin is used for an overcoat layer.

[0003] The production of a member using a pre-coated steel sheet is superior to the post-coating method in which a cold-rolled steel sheet or a plated steel sheet is processed into a member and then painted.
New characteristics are also being required. One of the problems is that when a member is manufactured by drawing, overhanging, stretching, or the like, the glossiness of a portion where the coating film elongates is reduced, and the appearance is not harmonized with other portions.

[0004]

The reduction in the gloss of the coating film is caused by factors such as roughening of the surface of the processed portion of the original coating plate, roughening of the coating film itself, and changes in the refractive index due to the molecular chain orientation of the coating film. It is caused by In order to solve such a problem, Japanese Patent No. 3162947 proposes a method of suppressing a decrease in gloss of a coating film by setting the elastic modulus of the coating film to a specific range. However, the above patent is an improvement only from the surface of the coating film, and does not consider the relationship between the coating layer and the coating layer of the original coating plate. Therefore, after processing, when the plating layer itself is roughened, the resin coating film follows the roughening of the plating layer, and irregularities are formed on the coating film surface. Was done.

The present invention has been devised in order to solve such a problem. In a coated steel sheet having a thermosetting resin coating film formed on a plated steel sheet, deformation of a plating layer and elongation of the coating film occur. Even if such processing is performed, it is difficult to form large irregularities on the plating layer, and even if small irregularities are formed, the coating film follows the coating so as not to form irregularities on the coating film surface. An object of the present invention is to provide a coated steel sheet whose film gloss is hardly reduced.

[0006]

Means for Solving the Problems The coated steel sheet having excellent drawability according to the present invention has an Al content of 2 to 2 in order to achieve the object.
The modulus of elasticity at 20 ° C. of the outermost resin coating film is 1 × 10 ^{3 to} 5 × 10 ³ N / mm ² on the plating layer of the molten Zn-based or Zn-Al-based plated steel sheet containing 65% by mass. A thermosetting resin coating film is provided.

[0007]

[Effects] (Plated steel sheet) In the conventional product, the following was found when the roughening of the plated layer, which is one of the factors that lower the glossiness of the processed portion, was examined. That is, in a normal hot-dip galvanized steel sheet or the like, when a crack is generated in a certain portion when stretched at the time of processing, since the components of the plating layer are uniform, stress concentrates there and grows into a large crack. . As a result, large irregularities easily occur. Further, in the alloyed hot-dip galvanized steel sheet, since the ductility of the plating layer is insufficient, large cracks are formed in the entire plating layer, and large irregularities are liable to occur.

On the other hand, in a hot-dip Zn-based or Zn-Al-based plated steel sheet containing Al to some extent, the plating layer
Since the rich layer and the Al rich layer exist in a sea-island state,
When stretched, micro cracks are preferentially generated at the interface between the Zn-rich layer and the Al-rich layer. The sea-island-like interface is uniformly dispersed on the plating surface, and stress is dispersed by generating fine cracks at various places, and many fine cracks are generated, but they do not grow into large ones.
Therefore, no large unevenness occurs.

A required for exhibiting the above effects
The l content is 2 to 65% by mass. If the Al content is less than 2% by mass, it is difficult for the Al-rich phase to separate into sea-island shapes, and if it exceeds 65% by mass, the effect is saturated. Coating weight of plating is not particularly limited, but it is sufficient per side 30g / m ² ~120g / m ² about the fact that workability is required. In addition, in addition to Zn and Al in the plating layer, corrosion resistance,
Various components such as Si, Mg, and misch metal may be added for the purpose of improving production stability and appearance.

(Overcoat) The overcoat has an elastic modulus at 20 ° C.
1x10 higher than before^Three~ 5 × 10^ThreeN / mm ^TwoStuff
There is no particular limitation. In order to provide workability,
Those having a film elongation of 20% or more are preferred. 1 × elastic modulus
10^ThreeN / mm^TwoThe plating layer of the original sheet
Even if the surface becomes rough, the coating film does not easily follow the unevenness, and the appearance is deteriorated.
Is unlikely to occur. In addition, the coating film itself is not easily roughened. Elastic modulus
Is 1 × 10^ThreeN / mm^TwoIf it is lower, the effect of suppressing gloss reduction will be reduced.
5 × 10 not obtained^ThreeN / mm^TwoToo high and coating film
The elongation is reduced, and the coating film is easily cracked.

In order to obtain the above-mentioned elastic modulus of the overcoated resin coating film, a molecular weight of 10,000 including a microcrystalline structure is required.
What is necessary is just to adjust by mix | blending a hardening | curing agent and a catalyst suitably to the high molecular weight polyester resin of 20,000. Regarding the film thickness, the range of the conventional precoated steel sheet of 10 to 25 μm is sufficient. Various additives such as a coloring pigment, an antibacterial material, a fungicide, a non-adhesive, and an antifouling agent may be added to the overcoat according to the purpose.

(Undercoat) The undercoat is not particularly limited, but has a higher modulus of elasticity than that of the prior art, as in the case of the overcoat, from 1 × 10 ^{3 to} 3.5.
It is preferable to set it in the range of × 10 ³ N / mm ² . As in the case of the top coat, by increasing the modulus of elasticity, even if the plating layer of the original plate becomes rough, the coating film hardly follows the irregularities, and the appearance does not easily deteriorate. When the elastic modulus is lower than 1 × 10 ³ N / mm ² , the coating film easily follows cracks in the plating layer, and the effect of suppressing a decrease in gloss cannot be obtained. Also, 3.5 × 10 ³ N / m
When it is too high exceeding m ² , the elongation of the coating film decreases, and the workability tends to decrease.

The elastic modulus of the undercoat resin film can be adjusted to the above value by appropriately mixing a curing agent and a catalyst with a high molecular weight polyester resin having a molecular weight of 10,000 to 30,000. 3 to 10μ
m of conventional precoated steel sheet is sufficient. Various additives such as rust preventive pigments, color pigments, extender pigments, and adhesion promoter pigments may be added to the undercoat coating film, regardless of whether they are chromium-based or non-chromium-based.

(Chemical conversion treatment and others)
It is preferable to perform a known chemical conversion treatment regardless of whether it is chromate or non-chromate. Before the chemical conversion treatment, if necessary, degreasing and surface conditioning may be performed. Paint baking is also performed in a conventional manner. The painting is a conventional roll coat, curtain coat,
Die coat, spray method, etc. may be used.
What is necessary is just to carry out by well-known heating means, such as an infrared furnace and an induction heating furnace.
The product configuration may be two coats or three coats.

[0015]

The present invention will be described below with reference to examples.
As a base plate, a cold rolled steel plate of titanium killed steel is subjected to hot-dip Zn-Al plating containing 5% Al and 55% Al, as compared with hot-dip Zn plated having an Al content of less than 2%, alloyed hot-dip Zn plating Prepared and hot-dip Al-plated (both having a plate thickness of 0.5 mm and a coating weight of 60 g / m ^{2 on} one side) were prepared and subjected to a coating type chromate treatment to give an elastic modulus of 8.4 × 10 ^3. N /
10 μm dry polyester film of mm ²
And baked at 215 ° C. for 40 seconds. Thereafter, polyester overcoats having various elastic moduli shown in Table 1 were applied to a dry film thickness of 20 μm, and baked and dried at 230 ° C. for 60 seconds. The coatability of the coated steel sheet thus obtained and the gloss change of the processed portion were evaluated in the following manner.

(1) Film workability Universal type deep drawing tester (Type 142-20 manufactured by Eriksen)
, Squeeze it into a square tube type (2 mm in length and width, 20 mm in depth), observe the crack state of the coating film at the corner with a magnifying glass with a magnification of 10 times. Those that were recognized were evaluated as ○, those that clearly showed cracks were evaluated as Δ, and those that saw cracks visually were evaluated as ×.

(2) Gloss retention (A) After deep drawing test The gloss of the unprocessed steel sheet and the square-drawing test piece subjected to deep drawing in the examination of the coating film processability was measured, and the gloss retention after processing was measured. Is 9
0% or more: 、, 80-89%: ○, 60-
79% was evaluated as Δ, and 59% or less was evaluated as ×.
(B) After tensile test, unprocessed steel plate and universal tensile tester (GT20 manufactured by Shimadzu Corporation)
00), the gloss of the test piece having an elongation of 15% was measured, and in the same manner as in the evaluation after the deep drawing test, those having a gloss retention of 90% or more after processing were evaluated as ◎, 80 to 89% was evaluated as 、, 60-79% as Δ, and 59% or less as X. Table 1 shows the results.

[0018]

As can be seen from the results, the overcoat resin film having an Al content of the plating layer within the range specified in the claims and having an elastic modulus of 1 × 10 ^{3 to} 5 × 10 ³ N / mm ² was obtained. The formed product of the example of the present invention was excellent in the processability of the coating film, and maintained the gloss before the process even after the process. On the other hand, even when the Al content of the plating layer is within the range specified in the claims, the one of Comparative Example 6 in which the elasticity of the top coating film resin is small has excellent workability, Following the surface roughening, the surface of the coating film became uneven, and the glossiness after processing was reduced.
In the case of Comparative Example 7 in which the elastic modulus of the overcoat film resin is large, both the processability and the gloss after processing are reduced. further,
It can be seen that all of Comparative Examples 8 to 10 in which the plating layer does not contain Al have poor workability and gloss retention.

[0020]

As described above, in a coated steel sheet in which a thermosetting resin coating film is formed on a plated steel sheet, a deep drawing or overhanging process is performed by using molten Zn containing Al as a coating original sheet. Also, by suppressing the formation of large cracks, that is, irregularities in the plating layer itself, and by setting the elastic modulus of the top coating resin coating to a predetermined value, even if small irregularities are formed in the plating layer, the top coating resin The film did not form irregularities on the surface of the coating film following the irregularities, and as a result, it was possible to suppress a decrease in appearance. As a result, it is possible to obtain a coated steel sheet in which the gloss of the coating film is hardly reduced even when a process involving deformation of the plating layer and elongation of the coating film is performed. A suitable prepainted steel sheet for deep drawing can be provided.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Tetsuo Sakai 7-1 Takaya Shinmachi, Ichikawa City, Chiba Prefecture Nisshin Steel Corporation Ichikawa Works F-term (reference) 4D075 BB87X BB91Z CA03 CA13 CA33 CB04 DA06 DB05 DC10 DC16 DC18 EA19 EB33 EB35 4F100 AA22 AB03A AB10A AB18A AK01B AK41 BA02 CA02 CC00B EH46 EH46B EH71A EJ65 EJ69 JB13B JK07B JL01 YY00A YY00B 4K027 AA05 AA22 AB05 AB26 AB28 AB44 AC26 AC73

Claims (1)

[Claims] 1. A coated steel sheet provided with a thermosetting resin coating film on a plating layer of a molten Zn-based or Zn-Al-based plated steel sheet containing 2 to 65% by mass of Al, wherein the outermost resin coating film Has an elastic modulus at 20 ° C. of 1 × 10 ^{3 to} 5 × 10 ³ N / mm ²
A coated steel sheet with excellent deep drawability and workability.